This invention relates generally to a hydro-mechanical transmission for a machine such as an agricultural combine or the like, and more particularly, to a hydro-mechanical transmission which, when in a neutral condition or state and fluid pressure is present, prevents or brakes driven rotation of the transmission output to limit undesired powered rotation of a rotatable operating element or elements connected thereto, but which preferably does not provide such braking effect when the fluid pressure is not present, thereby allowing manual rotation of the operating element or elements, as desired or required.
Currently, in known hydro-mechanical transmissions utilizing a mechanical power source and a fluid power source for operating rotatable elements, such as rotors, feeders and the like, of agricultural machines such as combines and the like, when placing the transmission in a neutral condition, it is typical to disengage a clutch connecting the mechanical power source to the transmission and move the variable pump or motor of the fluid power source to a zero displacement position, to break the power paths to the rotatable element or elements. However, a problem that has been observed, is that even though the clutch between the mechanical power source and the transmission is disengaged, as a result of normally present viscous drag, there may be sufficient hydraulic coupling or interaction between the clutch faces such that the mechanical input to the transmission is still driven to some extent. This condition may be more likely when the fluid is cold, such as when the engine is first started. As a result, the transmission output may be rotated, thus undesirably rotating the rotatable element or elements connected thereto. Particularly for the rotor and the feeder of an agricultural combine, it would be desirable to automatically prevent such inadvertent rotation, while still allowing manually rotating those elements when power to the transmission is not present, for inspection, service, installation, and the like.
It is long known to provide mechanical means for braking the rotation of an output of a transmission of an agricultural machine when disconnected from a power source. Reference in this regard, Rosenthal et al. U.S. Pat. No. 2,806,389 issued Sep. 17, 1957 to International Harvester Company, which discloses a power take-off mechanism for tractors including mechanical braking means which can be utilized for preventing rotation of an output of the mechanism when disconnected from a power source on the tractor. However, a resultant limitation of this mechanism is that the braking means must first be released for allowing manually or otherwise rotating the output and any rotatable elements connected thereto when input power is not present which would be undesirable for a rotor and feeder application as discussed above.
Accordingly, what is sought is a hydro-mechanical transmission for a machine such as an agricultural combine which provides an automatic output braking capability when in a neutral condition or state, but which still allows manual rotation of the transmission output and rotational elements connected thereto when input fluid power is not present.
According to the present invention, a hydro-mechanical transmission which provides an automatic braking capability as sought above, is disclosed. The preferred transmission includes a planetary gear arrangement having a rotatable output, a first rotatable input connected to an output of a fluid motor drivingly rotatable by passage of a flow of pressurized fluid therethrough, and a second rotatable input connected to a clutch or other suitable device engageable or operable for rotatably drivingly connecting the second input to a rotatable output of a mechanical power source, such as a gear box connected to an internal combustion engine. The transmission includes a fluid operated clutch, brake or other suitable device engageable or operable when fluid therein is pressurized for connecting the second input of the gear arrangement to a fixed member, such as a fixed frame or housing containing or supporting the gear arrangement, for preventing rotation of the second input. When the transmission is placed or moved into a neutral operating state or condition, the first clutch or other device is automatically disengaged or operated so as to disconnect the output of the mechanical power source from the second rotatable input of the gear arrangement, and at the same time, or in a desired sequence, the fluid clutch or brake or other device is automatically engaged or operated to connect the second rotatable input to the fixed member to prevent rotation of the second input, and passage of any flow of pressurized fluid through the fluid motor for drivingly rotating the motor is automatically prevented while or when the output of the mechanical power source is disconnected from the second input of the gear arrangement and the second input is connected to the fixed member, such that driving rotation of the output of the transmission is prevented.
A control for the transmission can include conventional fluid valving controlled by operator movable levers and/or handles, and/or an electronic control including a processor, operable for placing the transmission in the neutral operating state or condition upon receipt of a predetermined input representative of the neutral state or condition. The fluid motor can receive the pressurized fluid from any suitable source thereof, such as a fluid pump connected to the motor in a hydrostatic loop, either the motor or the pump having a variable displacement that can be zeroed for preventing pressurized fluid flow to or through the motor. Alternatively, a suitable pressure relief device can be provided in connection with the motor or elsewhere in the fluid connection thereto for depressurizing or otherwise preventing pressurized fluid flow thereto.
The present transmission has particular application for driving rotatable elements of agricultural combines, such as conveyor apparatus of a feeder thereof, and/or the threshing rotor or rotors thereof.
Advantageously, when the fluid in the fluid operated brake or other device is depressurized, the second input of the planetary gear arrangement is released from the fixed member, to allow manual rotation of the transmission output and rotatable elements connected thereto, such as a feed conveyor, rotor or rotors, to allow for installing, inspecting, or servicing the rotatable element or elements.